1. Field of the Invention
The invention relates to a rail joint assembly for joining rail ends together on railroad track and, more particularly, to a rail joint assembly more efficiently transferring both vertical and longitudinal railway loads through a strengthened rail joint.
2. Discussion of the Background
Early on, railroad operators butted rail ends together and mechanically fastened the rail ends together at the joint with joint bars on each side of the rail held in place by bolts through the web of each rail end.
A need arose to electrically isolate the rail ends from each other for train detection and for traffic control circuits that use the rail as conductors. Insulating adhesives such as epoxy have been used to both strengthen and to electrically isolate the two rail ends. U.S. Pat. No. 3,837,948 sets forth the use of both a thermoplastic adhesive layer which is itself normally electrically insulating to lock the rail ends together and an electrically insulating material such as resin-impregnated cloth. U.S. Design Pat. No. D547,642 shows a wrap-around joint bar sleeve insulator.
A number of prior rail joint designs are directed to approaches that strengthen the rail joint assembly and/or to insulate the two rail ends from each other. For example, U.S. Pat. No. 5,503,331 discloses a series of rail bonding adhesives using embedded nonconductive spacers. U.S. Pat. No. 7,090,143 uses an insulating spacer and a layer of epoxy that is sandwiched between a rail joint bar and the railroad rail. U.S. Patent Publication No. US2007/0272762 A1 (Ser. No. 11/420,199) sets forth joint bars with thicker midsections for use with thick web rail. The thicker midsection of the joint bar provides increased support for the joint at the abutment between the rail segments. U.S. Patent Publication No. US2008/0035749 A1 (Ser. No. 11/570,773) provides stiffener plates mounted to the joint bars such that the joint bars and the web portion of the rails are sandwiched between the stiffener plates.
A continued need exists to improve upon such joint designs because both mechanical and/or insulated joints have a lower service life than the rail itself. Generally insulated joints are replaced five to ten times during the service life of the rail and the resulting cost to replace failed mechanical or insulated joints is expensive. Additional costs are incurred due to service delays and service reliability. Rail joints constitute weak points in the track and are affected by railway loads passing over the joint which provide downward forces on the joint and by temperature variations. Railway loads, especially heavy railway loads, cause adhesive failure, failure of the mechanical fasteners, and failure of the joint bar. Wide swings in temperature also provide thermal stress to the rail joints. Insulated adhesive joints when subjected to such environmental stress and railway loads may lose strength. Such premature failures may cause one or more of the mechanical fasteners to then undergo mechanical stress resulting in shearing or cracking of the fastener.
Continuously welded rail (CWR) is used to eliminate the majority of rail joints, but rail joints, especially insulated rail joints, are still needed. The use of CWR has further increased the longitudinal loading on rail joints. Rail joint designs accommodate rail longitudinal movement by providing a space between the rail ends and oval holes in the joint bars. This space makes the joint less efficient in transferring both vertical and longitudinal loads through the joint. Insulated adhesives and mechanical fasteners are also subject to failure under such longitudinal stress as discussed above for vertical wheel loads.
Mechanical joints and Insulated joints represent two basic joints that act differently in the presence of longitudinal movement. Insulated joints do not allow for rail longitudinal movement and are inadequate to carry high longitudinal forces and high live railway loads. Mechanical joints allow for such longitudinal movement, but are weaker for carrying high vertical railway loads.
Three basic types of failure present in conventional mechanical rail joints are mechanical fastener failure, joint bar failure and rail battering. A fourth basic type of failure for insulated joints is adhesive failure. A need exists to provide a rail joint that more efficiently transfers vertical and longitudinal loads through the rail joint that substantially minimizes mechanical fastener failure, joint bar failure and adhesive failure. A need exists to strengthen a rail joint that approaches, equals, or exceeds the service life of the rail itself by substantially strengthening the rail joint assembly to handle railway load forces and environmental forces well exceeding those present.
An object of the invention is address the above needs by providing a rail joint assembly and method, for use with mechanical joints and insulated joints, having opposing pairs of load bearing keys embedded in both the rail web and in the joint bars that cause the web and the joint bars to integrally strengthen and act together, that effectively transfers vertical and horizontal railway loads through the joint and that intercepts the load path between the web and joint bars to minimize failure.